Nitazoxanide Is an Ineffective Treatment of Chronic Norovirus in Patients With X-Linked Agammaglobulinemia and May Yield False-Negative Polymerase Chain Reaction Findings in Stool Specimens

Tothe Editor—Thorne et al have recently reviewed antiviral therapeutic approaches for norovirus infection [1]. The authors concluded that nitazoxanide was the only compound to have undergone preliminary trial testing as a potential antiviral therapy for norovirus, having previously been shown to reduce symptom duration in immunocompetent patients, as well as to resolve symptoms in a single chronically infected patient [1, 2]. The use of nitazoxanide as a treatment for chronic norovirus infection, however, has not been reported since. Here we describe the failure of nitazoxanide treatment to eradicate chronic norovirus infection in a chronically infected patient with X-linked agammaglobulinemia (XLA), despite of initial polymerase chain reaction (PCR) analysis of a stool specimen that suggested virus eradication. Our patient with a genetically confirmed diagnosis of XLA initiated immunoglobulin replacement therapy at 12 weeks of age. At 10 years of age, he first presented with a diarrheal illness, which was confirmed to be norovirus associated, via findings of PCR analysis of a stool specimen. Norovirus infection persisted, resulting in chronic diarrhea and associated complications, including failure to thrive, pubertal delay, and nutritional deficiencies (in Fe, Cu, Zn, and vitamins A, D, E, and K). Multiple endoscopies with biopsy showed subtotal villous atrophy and intraepithelial lymphocytes; these histological findings have previously been described in patients with chronic norovirus infection [3]. Numerous treatment strategies aimed at augmenting the immune system in an attempt to clear norovirus infection or to control the chronic inflammatory process evident on intestinal biopsies have been studied. These strategies include oral budesonide; metronidazole and ciprofloxacin (as an empirical treatment for unidentified giardia or bacterial overgrowth); an increased parental immunoglobulin dose (2 g/kg/month); nasogastrically administered pentaglobin (25 mg/kg every 6 hours for 3 months [with a proton-pump inhibitor]); oral ribavirin; oral prednisolone; and melasalazine. A gluten-free diet (in view of the histological findings characteristically seen in celiac disease evident on duodenal biopsies) failed to provide any symptomatic improvement. Nitazoxanide was commenced at a dose of 500 mg twice daily. It was well tolerated with no adverse effects. Initially, an improvement in frequency and severity of diarrhea was noted. Results of PCR analysis of stool specimens became negative for norovirus; however, the MS2 bacteriophage used as an internal control added to the patient sample was also not detected by PCR, indicating inhibition of PCR. Dilution of the sample 1:100 prior to nucleic acid extraction overcame the inhibition, and both the norovirus and internal control became detectable by PCR in the diluted patient sample. Overall, 1% of feces samples that are tested in our laboratory demonstrate PCR inhibition, but consistent PCR inhibition over a series of samples, as seen in this patient, has not been seen before. Treatment with nitazoxanide was, therefore, discontinued after 12 months because of no clinical response and persistent detection of norovirus by PCR (after dilution). We believe that nitazoxanide was not inhibiting Taq polymerase within the PCR, as PCR analysis of feces specimens was consistently inhibited after nitazoxanide therapy was discontinued. Subsequent to treatment with nitazoxanide, a 12-week trial of ribavirin and pegylated interferon alfa and, separately, a further trial of enteral immunoglobulin via a jejunostomy failed to eradicate norovirus infection. This case demonstrates the lack of efficacy of nitazoxanide in treating chronic norovirus in an immunocompromised patient, despite previous reports of benefit [1]. Further clinical studies are required to establish the place of nitazoxanide in the treatment of norovirus in immunocompromised patients. Furthermore, the mechanism of the consistent PCR inhibition in this case is unclear. If it is a disease-specific effect, then it may be important to ensure that an internal control is being used in all fecal molecular assays for patients with XLA, to prevent false-negative results due to PCR inhibition. Potential conflicts of interest. All authors: No reported conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.